A multi-impression printer for pressure sensitive labels is disclosed in U.S. Pat. No. 4,111,121 to Borum. In the Borum printer, a supply roll of labels is unwound to advance a label through a first printer. The supply roll is further unwound to pass the printed label over a peeler roller and detach it from the carrier strip. As it is being detached, the leading edge of the printed label moves across an air gap and is reattached to a forward portion of the carrier strip. Between the detaching and reattaching stations a variable sized loop of carrier strip is formed, so that once reattached, further movement of the printed label occurs by movement of the carrier strip loop, without movement of the supply roll. The reattached label passes through a second printer and is dispensed.
The Borum multi-impression printer is not capable of high-speed on-demand label processing. This is because a label is moved through the first printer and to the detaching roller by unwinding the supply roll. Thus, by the time the printed label has been detached, the adjacent label has at least partially passed through the first printer as well. Clearly, processing cannot be on-demand if the adjacent label has already passed through the first printer during the printing and detaching of a first label.
Borum rewinds the supply roll after a label has been detached, to thereby return the adjacent label to a position upstream of the first printer. Thus, printing of the adjacent label need not occur until required, and the multi-impression printing may be performed in an on-demand fashion.
Unfortunately, reversing the supply roll after a label has been detached greatly slows down the label processor. A heavy supply roll of labels, having high inertia, requires a long time to reverse, accelerate and stop. This time lag degrades overall processor speed.
Reversal of the supply roll also introduces reliability problems into the label processor. As is well known to label users, the carrier strip often has cuts or nicks as a result of the label manufacturing operation. If such a cut or nicked roll is rapidly reversed, the carrier strip will tear, necessitating shut down and rethreading of the processor. Clearly, reversal of the supply roll is an unacceptable solution if high speed, reliable operation is required.
The prior art has also failed to solve the unique problems encountered in encoding magnetic information on labels. For example, precise inter-bit spacing cannot be attained when encoding takes place by unwinding the heavy supply roll to move a label past a magnetic encoding station. Moreover, the prior art has not provided efficient means for verifying the encoded information. Once the label has moved past the encoding station, reversal of the supply roll is necessary to bring the encoded label back through the encoding station for verification. Such reversal would degrade overall processing time as well as increase the possibility of tearing the carrier strip, as described above.